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#51
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SSB Antenna connection
On Wed, 26 May 2004 03:42:24 GMT, Bruce in Alaska
wrote: In article , "Steve (another one)" wrote: Dear Folks, What is the recommended wire to connect my insulated backstay to my AT-120 tuner ? I see references to GTO15 for this purpose in American publications, but no-one here in the UK seems to know what GTO15 is. Could someone please suggest an equivalent, or at least a description ! Also if the ground connection has to be broad copper strip because RF won't run down a wire like a conventional dc current, how can the antenna be wire ? Doesn't RF have to run along the cable to the base of the antenna and then up the antenna wire itself ? I'm confused ! Thanks for your help. Steve Others have covered the GTO-15 question, very well. There are a number of reasons that copper strap is used for RF Grounding in the Maritime Radio Installations. One being, that it is desireable for the RF Ground to have the lowest possible Impedance at the transmitted frequency. Two being, that it is desirable that the surface area of the RF Ground System be as large as practicable, to maximise coupling to the seawater. Three being, That RF flows on the surface of the conductor, and more surface area means lower impedance on the Ground. The antenna wire isn't supposed to couple into the seawater, but into the ethos, so it should have the least surface area as can practically handle the RF Current of the transmitter and be tuned to resonance by the tuner, and as low of resistance as practicable, so that RF Current can propagate along it's length. Bruce in alaska Gary S. can chime in anytime on this..... Hi Bruce, The diameter of the antenna wire is not too important. Actually the larger it is the less resistive loss it has and less power will be wasted in heat. But unless the antenna is significantly shorter than a quarter wavelength that loss is negligible in the antenna as the radiation resistance (radiation resistance is where the power goes to be radiated) is usually much higher than the resistive loss of the wire. However in a very short antenna the radiation resistance can be only an ohm or a few ohms. Then the resistance of the wire would be a larger percentage and the heat loss would be greater thus warranting a larger diameter wire. Otherwise a larger diameter wire has the advantage of greater bandwidth for given tuner settings. But the difference between #10 and # 16 would probably not be noticeable. As you well know, in the case of the ground system as we have said many times before, it needs to be as short as possible or it becomes part of the antenna and radiates. "The antenna starts at ground". Anything above ground is antenna. Regards Gary |
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SSB Antenna connection
On Fri, 28 May 2004 19:10:14 -0400, "Jack Painter"
wrote: "Chuck" wrote in message ... Bruce, I am asking why there is apparently such difference between feeding an ungrounded dipole with coax from an ATU (my shore station) and feeding an insulated (hence ungrounded) backstay from an ATU? I work Alaska bareback in the summertime with that setup and I just can't understand what GTO-15 does that hardline doesn't. If you could explain or reference a document that specifies the reasoning I would try to correct my misunderstanding. Thanks, Jack Painter Virginia Beach, Va If I can jump in, the quick answer is that the coax is approximately the same impedance as the center of your ungrounded dipole, at least at the frequency for which it is resonant. Thus, from the perspective of the transmitter and the antenna, the transmission line is "invisible." I'm exaggerating, of course. In the case of a backstay used as an antenna, the feedpoint impedance can be anywhere from a small fraction of an ohm at low frequencies to thousands of ohms where it approximates a half-wavelength. In those cases, the coax will most certainly not be invisible and will most likely either burn up or greatly attenuate your signal (incoming as well as outgoing, actually). If you tried to end-feed your half-wavelength dipole with coax, you would see a similar problem because the impedance at the ends is in the thousands of ohms range. Hope that helps. Chuck, as with Meindert's answer, yes that helps, thank you. I do end-feed a long wire as I said earlier, but it uses a 4:1 Balun, and additionally, has one side of that Balun shorted to ground. This is a noise-limiting design, and while the nice folks at Radio Works (Portsmouth, Va) maintain that it cannot possibly work this way (their Baluns), the CG aircraft I worked in Ecuador with it thought otherwise. So does it's designer, whose name slips my mind at the moment but he was a primary contributer to "Proceedings", and a Phd in EE with many patented antenna designs. Anyway, it would be interesting to see some modelling done with backstay antennas using various feedline approaches. I suspect the difference varies greatly with wavelength, height above ground (water), angle, and frequency. 73, Jack Painter Virginia Beach, Va Jack, Using a balun to feed an end fed wire may help and it may hurt the situation. It depends on the length of the wire verses frequency. If the wavelength is greater than a quarter wave length and the impedance of the wire is high, the balun will transform it down to a sometimes easier to match impedance. However if you use the antenna on different bands and you chose a band where the impedance of the antenna is low, then the 4:1 balun will step the impedance down even lower than the already low impedance of the antenna. It may well be that it is too low to match efficiently. As a general rule that type of balun is not a good idea when using that type of antenna on multiple bands. The only good a 1:1 balun would do with that type of antenna would be to decouple the feed line from the antenna (assuming coax feed line) and keep the feed line from radiating and or picking up unwanted signals. Regards Gary |
#53
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SSB Antenna connection
I am the one who posted that idea. I implemented it and used the setup on a
recent Mexico trip. I am a newbie in this arena, so I can only tell you that my rig was probably the best in the fleet of several boats. On the subject of antenna feed wire, I found an old reference on this NG recommending stripping the braid from coax(RG-8 is what I used) as a substitute for GTO-15. I was unable to locate a local source for GTO-15, so I went with the stripped coax. I was unable to do a good job on standoffs for the coax because of the hydraulics, but it didn't seem to matter a great deal. I did not think to do a helical wrap of the antenna wire which incidentally was just standard insulated #16 Ancor about 45' in length. On larger boats, the antenna wire is buried beneath the UV shield; on mine the wire was taped to the exterior of the UV shield. A lot of racing sailboats are switching their rod or wire backstays to Aramid at this time. The weight savings is dramatic, and the cost is roughly half of what a backstay with insulators would cost. I liked the idea, I saw here a while back, of using the new Kevlar based Backstay material, and not worring about having to ground or not. Seemed like the logical answer to me. Then just helical wrap the antenna wire around the Kevlar Backstay and have a really nice "Fully Loaded Antenna with alot of electrical length........ Bruce in alaska -- add a 2 before @ |
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SSB Antenna connection
"Gary Schafer" wrote
Oh boy! I just got back from vacation and am just now reading this stuff. Jack, Bruce and the others are entirely right. I once had a hard time figuring out why RF would not flow on the inside of a tube too. It would seem logical that it would do as you say but it doesn't. Look up "wave guide beyond cutoff". That will answer your question about why rf dose not flow on the inside of a tube. It will flow on the inside for only a very short distance from the opening. Then it gets canceled. This is how many signal generator attenuater work. They use a tube of 6 or so inches long with a sliding probe inside fed from one end. On the other open end is a fixed pickup probe. When the movable probe is close to the fixed probe on the other end, maximum signal coupling is obtained. As the other probe is moved away inside the tube the signal becomes highly attenuated. It is operating as a wave guide that is much too small for the frequency involved. If the tube diameter was made large enough to be a quarter wave length in diameter then the rf would propagate through it. But that would be in a different mode than the skin effect conduction being discussed. By the way did you know that skin effect even comes into play in 60 hz distribution systems? Regards Gary Hi Gary, welcome back, and thanks for your replies. Right principles, wrong application. Trying to apply high power microwave principles (3-15 gHz) to low power 2-30 mHz) is not the same. Now at 100 mHz and below, while there would still a small but measurable difference of skin effect at high transmit power, it ain't much and has nothing to do with low power 2-30 mHz where a thin walled copper tube has ZERO measurable difference in skin effect to a copper strap of even slightly smaller gage. That has been my never paid attention to point all along, that skin effect involves the entire cross section of thin material, and copper tubing is more than thin enough to carry current in it's entire (that means from outer to inner surface) cross section. That's exactly why copper tube is used so much in AM broadcast components. This is not even related to waveguides which must by design AVOID all skin effect which causes great resistance and heating at the current and velocites involved in microwave transmission. As we eventually got around to research rather than blindly arguing positions of opinion, then the participants hopefully learned something. I've learned that applying the math from formulas for skin effect in conductors of known ohmic value and used with a known frequency can determine the wall thickness of a conductor which has full cross sectional current on it. Guess what? The original poster's question about using copper tubing remains answered. A 1" copper tube has more surface area and carries just as much low power RF on it's entire cross section as a 1" wide piece of copper strap that is nearly the same gage. Best, Jack Painter Virginia Beach Va |
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SSB Antenna connection
Bruce in Alaska wrote in
: Hmmmm, all the PhdEE's that I asked, just laughed and ask how the weather and fishing was......... Bruce in alaska While you PhdEE's are on a roll, a little question...... A 6" wide, 1" thick solid copper strap 20 ft long connects an antenna tuner at the base of a 58' 3" insulated backstay on deck to a 30' long, 6" wide grounding block under the keel of a boat. What ground impedance does the tuner see on the 12 Mhz band? Larry W4CSC |
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SSB Antenna connection
Gary Schafer wrote in
: A good lightning ground is also a good RF ground. Welcome home, Gary. Missed your dissertations, really. Ah, but once again, BZZZT...WRONG..... I got two real-world examples to show you from my Navy experiences...... 1 - Aboard a wooden MSO (minesweeper, ocean), a sailor was nearly burned alive when he touched a metal handrail just outside the bridge while on watch! His hands had bad burns, as did his hip, which was touching a pipe not connected to the handrail. An electrical inspection found the handrail heavily grounded, per Navy requirements, to the boat's electrical grounding system, a good installation with no problems found. However, the burning continued. I found out about it from the boat's ET gang because I was in MINELANT's Mine Force Support Group electronics shop, at the time, around 1970? My EMO asked me my opinion and for me to take a look. Not far from the handrail was the antenna tuner and 35' whip of the boat's AN/URC-32 500W HF transmitter. Curious, I got a list of the frequencies the boat transmitted on the day he got burned. They operated only three that day, all on RTTY (FSK at full power). I took a tape measure and, as best we could, measured the length of the ground strap down into the bilge where it connected to the ship's grounding system. It was around 31 feet, total length, and didn't really connect to any other points on the way down into the engine room. One of the frequencies in question was on the 4 Mhz band just above the 75 meter ham band. At this frequency, the 31' ground strap was quite close to a 1/4 wavelength resonant ANTENNA with the open end right under our burned sailor's forearm and coffee cup he threw when the FSK started. So, let's test this theory. I took a scope probe with a 6' ground lead on it and connected the scope between the pipe he was leaning against, itself some length of antenna at some other frequency, and our burning handrail. "Key the transmitter.", I called down the passageway. WOW! The trace of the 4 Mhz RF was TOO BIG TO MEASURE! I could feel the RF in my fingers! So, moral, this great lightning ground was NOT ANYWHERE NEAR a good RF ground on 4 Mhz, or any other odd multiple of 1/4 wavelength. It was a resonant antenna with a handrail capacitor hat waiting to bite someone! Solution - After months of fighting the electrical engineers at NAVSEA about SHIPALTs to allow us to install them, we finally won and installed RF Chokes into all handrail grounds at the handrails themselves to keep them from becoming antennas resonant at any HF freq the ship used. 2 - Charleston Naval Shipyard, Metrology Laboratory of the Quality Assurance Office (Code 132.1). I was asked to look at a crazy alarm problem at the nuclear refueling docks where we pulled out the reactors from nuclear subs and replaced them with refuelled reactors. (The hulls are cut open and the core is swapped by a specially-equipped huge crane that runs on big rail tracks around the docks). Every time the crane lowered its big hook down into the hull, all the radiation alarms went crazy, even before the hook got to where it was supposed to go! Electrical Engineers (not RF engineers by a long shot) added more and more ground straps between the rails the huge crane sat on and the hull of the sub to "make sure" we had a "good ground" on everything. (More grounds were always their answer to everything.) I made arrangements to get the crane to where it would normally operate, with the operator at the controls, but with the hook first hanging over the rail of the crane, then over the hull of the sub in the drydock for testing. I snatched a portable Tektronix scope from the shop's inventory that was battery powered so it wouldn't be part of the grounding systems and met the crane at the appropriate time. I grounded the scope to the track at a handy pad eye used to hook the sub ground to it and as I approached this huge steel hook the trace on the scope went off my screen. My AC voltmeter read over 80VAC between "ground" and that hook. But wait! What's this MODULATION all about?? I ran back to the shop to retrieve my portable radio and quickly returned to the test point. Watching the AM modulation on my scope while tuning around on the AM band, I matched up the modulation envelope with WNCG AM 910Khz, a 5KW AM radio station some IDIOT at the FCC allowed them to construct right outside the hospital gate less than a mile from where I was standing. THE CRANE WAS A GIANT LOOP ANTENNA and I was standing at the high-impedance FEEDPOINT of that loop! Identifying the problem was easy. DOING something about the problem was NOT! NOONE in Rickover's Navy makes any CHANGES to anything without a fight. This fight I left, gladly, to much higher powers than me, but it also resulted in a huge strain insulator added to the cable of the crane to INSULATE the offending signal from the hook lowered into the sub. Wonder whatever happened to it, now that it's all gone bye-bye....?? Moral....a great lightning or AC line or DC ground is hardly EVER a good RF ground..... Ok, as usual, your turn..... Larry |
#57
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SSB Antenna connection
Gary Schafer wrote in
: The diameter of the antenna wire is not too important. Actually the larger it is the less resistive loss it has and less power will be wasted in heat. But unless the antenna is significantly shorter than a quarter wavelength that loss is negligible in the antenna as the radiation resistance (radiation resistance is where the power goes to be radiated) is usually much higher than the resistive loss of the wire. The diameter of the antenna wire is very important in the antenna's BANDWIDTH. Go by the CG shore station and look at how WIDE the conical monopole antenna is: http://www.tpub.com/content/et/14092/css/14092_35.htm The whole reason for the wide cone of these broadband HF antennas is to make it look as if the conductor were several FEET across to the RF from the feedpoint. Multiple, parallel conductors are also used to increase antenna wire apparent diameter in broadband rhombic antennas such as: http://www.smc-comms.com/rhombic_antenna.htm To quote the text: "The simple one wire system has a bandwidth of approximately 2: 1, however SMC have wide experience in the design of this type of antenna and are able to offer arrays with 1, 2 or 3 wires per leg to give a bandwidth of up to 4: 1 and, by careful design, gains of 22 dBi are possible." However in a very short antenna the radiation resistance can be only an ohm or a few ohms. Then the resistance of the wire would be a larger percentage and the heat loss would be greater thus warranting a larger diameter wire. Huh?? ANY antenna under 1/4 wavelength long exhibits HIGHER and HIGHER impedance the SHORTER it gets. The first low impedance of a wire antenna occurs when its radiator (against a ground, artificial or real) is 1/4 wavelength long. A very short antenna, i.e. a 6' whip on the handrail, has a very HIGH impedance as frequency decreases on the HF band. That's why we use an L network to match it to 50 ohms....coil in series, cap to ground to lower its impedance. Otherwise a larger diameter wire has the advantage of greater bandwidth for given tuner settings. But the difference between #10 and # 16 would probably not be noticeable. True, that's why we use multiple parallel conductors above. As you well know, in the case of the ground system as we have said many times before, it needs to be as short as possible or it becomes part of the antenna and radiates. "The antenna starts at ground". Anything above ground is antenna. Actually, in a plastic boat, the radiation from the ground strap is useful radiation. You've just moved the FEEDPOINT up the radiating element above the sea. My feedpoint is about 4.8' above ground on Lionheart. It's signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil, most of Western Europe on 40 meters and 20 meters. Works pretty good! 73, Larry W4CSC |
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SSB Antenna connection
On Tue, 8 Jun 2004 17:05:53 -0400, "Jack Painter" wrote: "Gary Schafer" wrote Oh boy! I just got back from vacation and am just now reading this stuff. Jack, Bruce and the others are entirely right. I once had a hard time figuring out why RF would not flow on the inside of a tube too. It would seem logical that it would do as you say but it doesn't. Look up "wave guide beyond cutoff". That will answer your question about why rf dose not flow on the inside of a tube. It will flow on the inside for only a very short distance from the opening. Then it gets canceled. This is how many signal generator attenuater work. They use a tube of 6 or so inches long with a sliding probe inside fed from one end. On the other open end is a fixed pickup probe. When the movable probe is close to the fixed probe on the other end, maximum signal coupling is obtained. As the other probe is moved away inside the tube the signal becomes highly attenuated. It is operating as a wave guide that is much too small for the frequency involved. If the tube diameter was made large enough to be a quarter wave length in diameter then the rf would propagate through it. But that would be in a different mode than the skin effect conduction being discussed. By the way did you know that skin effect even comes into play in 60 hz distribution systems? Regards Gary Hi Gary, welcome back, and thanks for your replies. Right principles, wrong application. Trying to apply high power microwave principles (3-15 gHz) to low power 2-30 mHz) is not the same. Sorry Jack but you are wrong. It has nothing to do with microwave frequencies. A wave guide beyond cutoff is the mode that the tube is operating in and it simply tells you that the frequency is too low for the given size tube to propagate through. The energy inside the tube gets shorted out. Many 2-30 mhz signal generators use that type attenuator. Now at 100 mHz and below, while there would still a small but measurable difference of skin effect at high transmit power, it ain't much and has nothing to do with low power 2-30 mHz where a thin walled copper tube has ZERO measurable difference in skin effect to a copper strap of even slightly smaller gage. It has everything to do with it. Skin effect is ever present in all conductors at ALL frequencies. Note my reference to 60 hz power transmission where it is also important. That has been my never paid attention to point all along, that skin effect involves the entire cross section of thin material, and copper tubing is more than thin enough to carry current in it's entire (that means from outer to inner surface) cross section. That's exactly why copper tube is used so much in AM broadcast components. That is a contradiction to your point. You say that current flows entirely through the walls of copper tubing and then say that is why it is used in AM broadcast components. If that were true then they would not use copper tubing but instead they would use solid copper rod for better conduction. The reason copper tubing is used is that there is no current of any significance past a certain depth and to use solid rod would be a waste of copper. This is not even related to waveguides which must by design AVOID all skin effect which causes great resistance and heating at the current and velocites involved in microwave transmission. Well, microwave transmissions don't travel any faster than HF transmissions. But you might note that most wave guide inner surfaces are silver plated to reduce skin losses. As we eventually got around to research rather than blindly arguing positions of opinion, then the participants hopefully learned something. I've learned that applying the math from formulas for skin effect in conductors of known ohmic value and used with a known frequency can determine the wall thickness of a conductor which has full cross sectional current on it. Guess what? The original poster's question about using copper tubing remains answered. A 1" copper tube has more surface area and carries just as much low power RF on it's entire cross section as a 1" wide piece of copper strap that is nearly the same gage. While skin effect is a gradient and not an absolute barrier, there is current that flows at all levels in a conductor. Even on the inner surface of your copper tube. But the amount of current there is so small that it is immeasurable. It decreases exponentially. One skin depth is defined as the depth at which the current has dropped to about .37 times the current at the surface. (If you notice, this is the same decay rate that a capacitor has when it charges or discharges.) When you go that same distance (deeper) again the remaining current will again drop to .37 times the current that it was at the first skin depth. So you can see that the current never reaches zero as you go deeper but it only takes a few skin depths to decrease the current to a very small value which is insignificant. ..0058" is the skin depth in copper at 200 khz. Skin depth decreases by 10 for each 100 times increase in frequency. So at 20 mhz the skin depth would decrease by 100 from that. It gets pretty thin! Skin effect is the reason coax cable works as it does. None of the RF on the inside of the cable appears on the outside of the cable. Other than leakage between strands of the shield of the cable. Those wire strands on coax cable are pretty thin. Much thinner than your copper pipe. Hard line has no leakage. Regards Gary Best, Jack Painter Virginia Beach Va |
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SSB Antenna connection
On Tue, 08 Jun 2004 23:39:09 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : A good lightning ground is also a good RF ground. Welcome home, Gary. Missed your dissertations, really. Ah, but once again, BZZZT...WRONG..... I got two real-world examples to show you from my Navy experiences...... 1 - Aboard a wooden MSO (minesweeper, ocean), a sailor was nearly burned alive when he touched a metal handrail just outside the bridge while on watch! His hands had bad burns, as did his hip, which was touching a pipe not connected to the handrail. An electrical inspection found the handrail heavily grounded, per Navy requirements, to the boat's electrical grounding system, a good installation with no problems found. However, the burning continued. I found out about it from the boat's ET gang because I was in MINELANT's Mine Force Support Group electronics shop, at the time, around 1970? My EMO asked me my opinion and for me to take a look. Not far from the handrail was the antenna tuner and 35' whip of the boat's AN/URC-32 500W HF transmitter. Curious, I got a list of the frequencies the boat transmitted on the day he got burned. They operated only three that day, all on RTTY (FSK at full power). I took a tape measure and, as best we could, measured the length of the ground strap down into the bilge where it connected to the ship's grounding system. It was around 31 feet, total length, and didn't really connect to any other points on the way down into the engine room. One of the frequencies in question was on the 4 Mhz band just above the 75 meter ham band. At this frequency, the 31' ground strap was quite close to a 1/4 wavelength resonant ANTENNA with the open end right under our burned sailor's forearm and coffee cup he threw when the FSK started. So, let's test this theory. I took a scope probe with a 6' ground lead on it and connected the scope between the pipe he was leaning against, itself some length of antenna at some other frequency, and our burning handrail. "Key the transmitter.", I called down the passageway. WOW! The trace of the 4 Mhz RF was TOO BIG TO MEASURE! I could feel the RF in my fingers! So, moral, this great lightning ground was NOT ANYWHERE NEAR a good RF ground on 4 Mhz, or any other odd multiple of 1/4 wavelength. It was a resonant antenna with a handrail capacitor hat waiting to bite someone! Solution - After months of fighting the electrical engineers at NAVSEA about SHIPALTs to allow us to install them, we finally won and installed RF Chokes into all handrail grounds at the handrails themselves to keep them from becoming antennas resonant at any HF freq the ship used. 2 - Charleston Naval Shipyard, Metrology Laboratory of the Quality Assurance Office (Code 132.1). I was asked to look at a crazy alarm problem at the nuclear refueling docks where we pulled out the reactors from nuclear subs and replaced them with refuelled reactors. (The hulls are cut open and the core is swapped by a specially-equipped huge crane that runs on big rail tracks around the docks). Every time the crane lowered its big hook down into the hull, all the radiation alarms went crazy, even before the hook got to where it was supposed to go! Electrical Engineers (not RF engineers by a long shot) added more and more ground straps between the rails the huge crane sat on and the hull of the sub to "make sure" we had a "good ground" on everything. (More grounds were always their answer to everything.) I made arrangements to get the crane to where it would normally operate, with the operator at the controls, but with the hook first hanging over the rail of the crane, then over the hull of the sub in the drydock for testing. I snatched a portable Tektronix scope from the shop's inventory that was battery powered so it wouldn't be part of the grounding systems and met the crane at the appropriate time. I grounded the scope to the track at a handy pad eye used to hook the sub ground to it and as I approached this huge steel hook the trace on the scope went off my screen. My AC voltmeter read over 80VAC between "ground" and that hook. But wait! What's this MODULATION all about?? I ran back to the shop to retrieve my portable radio and quickly returned to the test point. Watching the AM modulation on my scope while tuning around on the AM band, I matched up the modulation envelope with WNCG AM 910Khz, a 5KW AM radio station some IDIOT at the FCC allowed them to construct right outside the hospital gate less than a mile from where I was standing. THE CRANE WAS A GIANT LOOP ANTENNA and I was standing at the high-impedance FEEDPOINT of that loop! Identifying the problem was easy. DOING something about the problem was NOT! NOONE in Rickover's Navy makes any CHANGES to anything without a fight. This fight I left, gladly, to much higher powers than me, but it also resulted in a huge strain insulator added to the cable of the crane to INSULATE the offending signal from the hook lowered into the sub. Wonder whatever happened to it, now that it's all gone bye-bye....?? Moral....a great lightning or AC line or DC ground is hardly EVER a good RF ground..... Ok, as usual, your turn..... Larry Hi Larry, Hope you had a good sail. Well this is an easy one! Your hand rail was not a good lightning ground even though it may have had a large ground strap connected to it. The path to ground was too long providing a high impedance. Same for the crane. Too long a ground lead at the hook. A good lightning ground has to have a low DC resistance as well as a low impedance to AC. Remember that lightning has a large AC component that is very strong. Any impedance in it's path despite how well the DC ground may be will allow a large voltage to develop on it. A good antenna ground must also have a low impedance. Regards Gary |
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SSB Antenna connection
I'm having trouble imaging a 6" wide by 1" thick piece of
copper as a "strap" Doug, k3qt s/v Callista "Larry W4CSC" wrote in message ... Bruce in Alaska wrote in : Hmmmm, all the PhdEE's that I asked, just laughed and ask how the weather and fishing was......... Bruce in alaska While you PhdEE's are on a roll, a little question...... A 6" wide, 1" thick solid copper strap 20 ft long connects an antenna tuner at the base of a 58' 3" insulated backstay on deck to a 30' long, 6" wide grounding block under the keel of a boat. What ground impedance does the tuner see on the 12 Mhz band? Larry W4CSC |
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